1. Field of the Invention
The present invention is generally related to an outboard motor with an idle relief conduit and, more particularly, to an outboard motor with an idle relief system that is selectively controlled as a function of an operating condition of the engine, such as its operating speed.
2. Description of the Related Art
Those skilled in the art of outboard motor design and manufacture are very familiar with the concept relating to an idle relief conduit. Typically, a primary exhaust path discharges exhaust from an engine to a location below the surface of a body of water. This is done for several reasons, including noise reduction, which are very familiar to those skilled in the art. Many types of outboard motors also include an idle relief system that allows exhaust to be emitted above the surface of the body of water. The purpose of the idle relief system is to allow exhaust to be emitted, when the engine is operating at idle speed, without causing the engine to labor unnecessarily to force the exhaust to overcome the pressure caused by standing water within the outboard motor through which the exhaust gas must pass in order to be emitted below the surface of a body of water. Those skilled in the art of marine propulsion systems are very well aware of many different types of systems that accomplish these purposes.
U.S. Pat. No. 4,668,199, which issued to Freund et al. on May 26, 1987, discloses an idle exhaust relief system for outboard motors. It includes a main exhaust passageway extending through a partially filled water chamber in the driveshaft housing. An inlet idle relief passage connects the top of the chamber with the main exhaust passageway and an outlet passage connects the top of the chamber with the atmosphere. The system defines an effective exhaust silencer for the idle exhaust.
U.S. Pat. No. 5,041,036, which issued to Clark et al. on Aug. 20, 1991, describes an idle exhaust gas relief arrangement for an outboard motor. The outboard motor comprises an internal combustion engine including a lower surface having therein an exhaust gas discharge port, a driveshaft housing having an upper end including an upper face fixed to the lower surface of the internal combustion engine, an outer surface extending downwardly from the upper face, an interior vertically extending main exhaust gas passage extending from the upper face and communicating with the exhaust gas discharge port, and an idle exhaust gas relief passage recessed in the upper face and in spaced relation to the main exhaust gas passage.
U.S. Pat. No. 5,348,500, which issued to Lassanske on Sep. 20, 1994, describes a marine propulsion device with selectively operable secondary exhaust discharge. It comprises a powerhead including an internal combustion engine having an output shaft and an exhaust port, a propeller shaft adapted to hold the propeller, a selective coupler of the engine output shaft and a propeller shaft, an exhaust passage communicating with the engine exhaust port and comprising a first exhaust outlet and a second exhaust outlet, and a valve that is associated with the selective coupler to open and close the second exhaust outlet.
U.S. Pat. No. 5,524,578, which issued to Craft et al. on Jun. 11, 1996, describes a two-cycle engine having an improved idle relief system. The engine has an engine block defining at least two cylinders having respective cylinder heads. Pistons are reciprocal within respective ones of the cylinders. The cylinders have respective fuel inlet ports and exhaust ports and two of the cylinders have an idle relief port disposed between their respective exhaust port and head ends.
U.S. Pat. No. 7,001,231, which issued to Halley et al. on Feb. 21, 2006, discloses a dual water injector for primary and idle relief exhaust passages. A water cooling system for an outboard motor provides a water conduit that extends through both an idle exhaust relief passage and a primary exhaust passage. Water within the water conduit flows through first and second openings to distribute sprays or streams of water into first and second exhaust conduits which can be the primary and idle exhaust relief passages of an outboard motor.
The patents described above are hereby expressly incorporated by reference in the description of the present invention.
The flow of exhaust gas through an idle exhaust relief conduit can emit noise, particularly when the engine is operated at relatively high speed. When a marine vessel is operating at elevated speeds, above idle speed, many types of engines continue to conduct exhaust gas through the idle exhaust relief conduit even though the engine is no longer operating at idle speed. This emission of exhaust through the idle relief conduit is above the surface of the body of water on which the marine vessel is operated and, therefore, is not muffled by being emitted below the surface. As a result, noise emission from the idle exhaust relief conduit can diminish the enjoyment of the use of the marine vessel. Some outboard motors provide silencers in conjunction with the idle exhaust relief conduit. However, it would be significantly beneficial if a system could be provided which inhibits the flow of exhaust gas through the idle exhaust relief conduit when the engine of an outboard motor is operated above a preselected level, such as idle speed.